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Home Energy Monitor


How do these things work? What would it take to make one?

Home Energy Monitor



It is done in 2 parts:

  1. read the current consumed by a device. Here are some good examples

  2. present the data to the user, on a display or through network. This one is easily covered in NETMF and GHI’s product line.


I read the “How Does It Works” section on the web site and it indicates that some sort of sensor is attached to the outside of the electrical power meter to sense “in real time” how much electricity is being used. The sensor transmits it’s data wirelessly to a ‘base’ unit that displays (and collects) the data.

I think the the hardest part would be to find a sensor to read the electric meter. Once a suitable sensor was found the rest should be relatively easy to do.



There is a nice DIY project called “Tweet-a-Watt”. Look it up:


After some research, it looks like the meter is optical. It seems to read the spinning disc on the meter.

I know about tweet-a-watt. I have some of the kill-a-watt meters. They are not whole house though. I want to monitor the entire house. I may just buy one of the seedstudio devices. That seems like a good approach for the whole house.


there’s another thread on this here:

The folks at Smart Energy Groups use the same concept as most of the commercial meters, like the efergy, and use current clamp meters to detect the current flow from key areas. In my case I have 3-phase power, so as a minimum I need to clamp three wires to measure “total” consumption. Stacy, you may also need more than one, but at least one gives you something you can prove the concept with!

My “ideal world” thought from the other thread is still where I’d like to get to; that project isn’t on my radar yet :frowning:


Great info Brett! Thanks!


The Blue Line sensor works by measuring how many times the disk spins on your meter. If you go out to your meter and stare at it for a little bit, you’ll notice that there is a black marking on your meter. The sensor uses an optical reflector to determine when the black mark is in front of it. It measures the velocity of the disk and can make updates between revolutions in “real time”.

On the display part, you input your billing information so that it can calculate how much your energy bill is going to be. I’m not sure how well the sensor side would work with the AMR (automatic meter reading) systems that are installed on a lot of homes now days, they use the same principle and the new sensor may not fit in conjunction with the old one.

You could always get a current sensing probe, but you will have to calculate the kw/hr on your own, as the sensors will only tell you the instantaneous amperage draw. You can make some assumptions on the power side, like there is always 120VAC going into your house, but that’s not always true, it can run from 110 to 125 depending on how close you are to big current draws (like factories)…

Here is a good source of high amperage current sensors:

Another challenge you will have is the data communication to the display station. You can use standard WiFi, or you can use some other 2.4/9.8ghz devices that are easy to use. I would recommend XBee or ZigBee, as they are easy to use and basically send data like a serial port, not to mention they are a little more secure than just broadcasting your power consumption to all your neighbors adhoc.

Looks like a fun project.